Effect of Monomer Sequence along Network Chains on Thermoresponsive Properties of Polymer Gels.

Shohei Ida,Hidekazu Kawabata,Tatsuya Ishikawa,Toru Kawahara,Yoshitsugu Hirokawa

doi:10.3390/gels4010022

Abstract

The effect of monomer sequence along the network chain on the swelling behavior of polymer gels should be clarified for the advanced control of swelling properties of gel materials. To this end, we systematically investigated the swelling properties of poly(acrylamide derivative) gels with the same composition but different monomer sequence by utilizing two gel synthetic methods: copolymerization giving a random network and co-crosslinking giving a blocky network. Both of the copolymerization and the co-crosslinking gels were prepared from the combination of two of the three following monomers: hydrophilic N,N-dimethylacrylamide (DMAAm), hydrophobic N-n-butylacrylamide (NBAAm), and thermoresponsive N-isopropylacrylamide (NIPAAm) with various monomer compositions. The swelling measurement of the obtained gels showed totally different behaviors between the copolymerization and the co-crosslinking gels, even with the same monomer composition. The copolymerization gels had the average property from the two monomers, depending on monomer composition, because random monomer distribution changed the affinity of each network chain to water. On the other hand, the co-crosslinking gels behaved as if two components independently contributed to the swelling properties, probably due to the domain structure derived from two kinds of prepolymers.

Highlights

Since the discovery of volume phase transition of polymer gels by Tanaka et al [1,2,3], research on stimuli-responsive gels has been actively conducted
The thermoresponsive property in water originates from the balance of hydrophilicity and hydrophobicity in the network chains: the former dominates the hydration at low temperature and the latter affects the aggregation of hydrophobic groups at high temperature
We evaluated the effect of monomer sequence along the network chain of polymer gels on the swelling behavior by utilizing two gel synthetic methods: copolymerization and co-crosslinking

Summary

Introduction

Since the discovery of volume phase transition of polymer gels by Tanaka et al [1,2,3], research on stimuli-responsive gels has been actively conducted. The most representative example is poly(N-isopropylacrylamide) (PNIPAAm) gel, which shows phase transition at around 33 ◦ C in pure water and is anticipated to be useful in various applications [3,4,5,6,7,8,9]. The thermoresponsive property in water originates from the balance of hydrophilicity and hydrophobicity in the network chains: the former dominates the hydration at low temperature and the latter affects the aggregation of hydrophobic groups at high temperature. An appropriate design of hydrophilicity/hydrophobicity balance in the structure is required for the control of thermoresponsive properties. A general approach to control the swelling properties of polymer gels is the combination of plural monomers by copolymerization.

Methods

Results

Conclusion